Shivering in his sleeping bag on a park bench in central London, student Leon Rossi felt helpless. It was December – supposedly the season of goodwill – yet he had been turned away from every hostel in King’s Cross. He was 26 and in good health, which put him at the bottom of the priority list for getting a bed.

“It was frightening and unbelievably lonely,” he says. “I couldn’t sleep at night. All I could think about was how to survive.”

Seven years on Leon, who features in forthcoming Channel 4 documentary The Great British Property Scandal, now has a spacious, one-bedroom flat in Finsbury Park. It’s rented to him by Real Lettings, a social enterprise that takes on abandoned or empty properties and lets them out to vulnerable people who are ineligible for social housing.

“I feel like a human being again,” Leon says. “I don’t have to watch my back the whole time.”

Like countless other young men and women who end up sleeping rough, Leon had been living a normal existence before he lost his home. He wasn’t a drug user or a criminal. He was studying English at college. He had a part-time job and a social life.

But over the course of a few months his life had fallen apart. He’d been made redundant, defaulted on his rent, and then he’d lost his council house. Initially he slept on the sofa at his mother’s home, but three months later, still without a job and having exhausted the generosity of his relations, he took to the streets.

“My family have their own children to look after,” he says. “I felt like a burden just using their facilities.” With nowhere to live, he dropped out of his course. It’s only now, with a kitchen table to work at, that he’s in a position to resume it.

Leon’s story is remarkably common. According to Phil Spencer, who presents the Channel 4 documentary and is the patron of homelessness charity Broadway, most of us are only three pay cheques away from losing our homes. Between November 1 and December 25 an estimated 35,000 will face homelessness, according to the charity, Shelter. “People assume homeless people are down and outs, but more often than not they’ve just had a couple of bad rolls of the dice,” says Spencer.

If you’re a woman, a teenager, elderly or infirm your chances of a bed in a hostel or social houses are higher. But healthy young men must wait weeks, sometimes months, before they’re given a place in a hostel. And they can forget about their own social housing until they’ve turned 35. Right now there are two millions families in Britain in need of a decent home, and they take priority. “For homeless young men the outlook is increasingly bleak,” says Spencer.

But there are countless flats lying empty and abandoned, which could, with minimum effort, provide a home for someone living on the streets. Leon’s flat is a case in point. Before Real Lettings took it on, it had been empty for a while.

Real Lettings, which is an arm of Broadway, uses grants from local councils to restore such properties, before renting them out to vulnerable people, who pay the rent with housing benefits. “It’s completely barmy that anyone lives out on the streets when there are so many empty homes,” Spencer says.

In Britain there are an estimated 350,000 long-term empty properties, but the figure is probably much higher. Apartments above a shop, like Leon’s, account for 20 per cent of abandoned homes. Yet they don’t necessarily fall under the Housing Act, so they’re not recorded by local authorities. Most councils have an empty property officer who can help find a use for an abandoned home. In extreme cases a council can even make a compulsory purchase on an empty property. But it is complicated to bring an empty property back into habitation, even if you’re a council or a housing trust. It’s certainly not something someone living on the street is in a position to sort out.

In the documentary, Spencer will call for the government to make it easier for ordinary people to get empty homes back in use.

“We have a housing problem in Britain. If you look at the number of people and the number of houses it doesn’t add up. And the situation is getting worse,” he says. It’s not just flats above shops, and boarded-up terrace houses, that are going spare. New-build social housing and private developments across the country have been victim to the recession, and are now lying unfinished or abandoned, with habitable properties standing empty.

This doesn’t need to be the case, Spencer insists. Schemes such as Real Lettings take a property out of a landlord’s hands, offer a guaranteed rental income for three years and a full management service. So far 88 per cent of landlords have renewed their lease with Real Lettings, even though they are taking a lower weekly rent than they would on the private market.

“It’s hassle-free,” says Howard Sinclair of Real Lettings. “Even the most difficult property to rent out can become a secure investment.” Real Lettings only operates in London. Landlords in other areas can lease their properties to the council or a housing association, who will act as a managing agent; finding tenants, collecting rent, and arranging repairs and maintenance, usually in return for one month’s rent per year. (More information see www.emptyhomes.com.)

Whilst making the documentary, Spencer test drove the concept when he persuaded a 90-year-old shopkeeper to allow a building team into two abandoned flats above his business in Turnpike Lane. “The owner didn’t want to do anything with them himself,” explains Spencer. “They’d have stood empty indefinitely.” The flats are now homes for two former rough sleepers. “It’s a win-win scheme,” says Spencer. “The owner gets rent for the first time ever. The council removed two homes from the empty homes register which earned it a reward from the government, and two rough sleepers have a home by Christmas.”

On the first night in his new flat, Leon bunked down on the floor. He would have continued to live in this way - out of habit more than anything else - if Broadway hadn’t insisted he got a bed. “If someone’s been living on the streets for months, or in a hostel dormitory, you can’t just expect to hand them the keys to a flat and expect to get on with it,” says Spencer. “They need support; they need to relearn how to manage their life; how to claim their housing benefits and keep up to date with bills.” A large part of the charity’s work is helping homeless people settle in to their new abodes, to provide basic furniture and bedding, and to encourage them to make something of their future once they’ve got somewhere to live.

Spencer hopes The Great British Property Scandal programmes will highlight the importance of getting young people off the streets as quickly as possible.

Leon has now lived in Finsbury Park for three years. He pays his rent with local housing benefits, and hasn’t defaulted once. “I’m happy here and I feel secure,” he says. He’s now a trained security guard, and he hopes to start studying again next year once he’s saved some money. Anyone sleeping rough this Christmas should, he says, hold on to the dream of having their own home. “You’ve got to keep believing and it will happen,” he says.

It will, agrees Phil Spencer, but only if we work harder to find housing for those whose lives have taken a wrong turn. “I want to see more young men getting their lives back on track. It wouldn’t take much for Leon’s story to become the norm.”